The aims of this proposal bear directly on our understanding of the central organization of the vertebrate auditory and vestibular systems. Two questions are asked: (1) Do land vertebrates possess a second auditory pathway arising from inner ear endorgans other than the cochlea? (2) Are the termination sites of eighth nerve fibers originating in the cochlea co-extensive with those originating from other inner ear endorgans? These data should provide insight into the question of how major changes in the sensory periphery, in this case the addition of new auditory endorgans, are reflected in the organization of central neural pathways. Experimental tract tracing techniques, such as horseradish peroxidase and autoradiography, will be applied to portions of the eighth nerve subserving various inner ear endorgans. The roles of some of these endorgans are poorly understood at present, and these data will provide insights into their functions in all vertebrates, including mammals.